Quick Links

Two switch options Manual: Typically found with larger portable generators, these transfer switches are used to disconnect the service panel manually from the grid and connect it to the generator, often via an exterior inlet. Managing loads becomes easier, and there are no extension cords. However, fueling and capacity for the generator are still a consideration. Automatic: Limited to permanently installed standby generators with dedicated fuel hookups, an automatic transfer switch and controller monitors the house’s incoming electricity. If voltage from the grid drops, the generator turns on, and the electrical panel automatically switches over to generator power. This system also monitors the electrical grid and automatically switches back to normal utility power when power is restored. 20kw 50kw 4 Prioritizing circuits Large homes with big but still undersize generators that need to manage the load of more than six appliances can use a loadshedding transfer switch. One example of these expensive switches—Generac’s $1500 Nexus LTS—has 16 circuits for powering priority items. The transfer switch will also power the remaining circuits in the main panel and monitor the frequency (Hz.) of the current, which in North America is supplied at 60 Hz. If current falls below 57 Hz. (typically caused by high start-up loads), the switch will shut off all nonessential circuits to keep the priority items running. After a delay, the nonessential circuits are brought back online. GE’s Symphony II ($1200) is intended to back up the whole service panel by having you prioritize appliances. When the generator approaches maximum load, it sheds the lowest priority circuits one at a time until there’s capacity available to power the highest priority circuit. Once demand falls, lower priority circuits are brought back online. $6000 5 Worry free Switches for whole-house protection are relatively basic, but they require a generator large enough to handle all the loads in the house, including their respective start-up loads. These service-rated transfer switches ($600 to $1000) shift the entire service panel over to generator power. It may still make sense to use a switch with dedicated AC-load management to reduce stress on the generator. $12,000 limited in the number of items you can run both by the output rating of the generator and by the number of outlets. Finally, small fuel capacity means that you need to have a large quantity of gasoline on hand for anything but the briefest power interruption. The next step in backup power relies on a larger portable generator—typically a unit on wheels—that energizes the house’s circuits through the service panel. This scenario requires a manual transfer switch to disconnect the service panel from the grid and to connect it to the generator, often via a permanently installed exterior inlet. While the generator’s output rating still limits the number of circuits you can power, these wheelbarrow-style portable units come in sizes large enough to power an HVAC system, critical appliances, and lights. With the transfer switch, you can manage the load by switching circuits on and off. Of course, you still have fueling issues, and maintenance routines include testing the engine monthly. For automatic power, you need a padmounted, permanently installed outdoor generator. Depending on the output size, a standby system can be configured to power either essential circuits or the entire house. The key to the system is the automatic transfer switch. A controller monitors the electricity coming into the service panel. If the supply is interrupted or the voltage drops below 60% (known as a “brownout”), the generator’s engine starts. After a brief engine warm-up (about 10 seconds), the transfer switch disconnects the service panel from the grid and shifts to generator power. The controller continuously monitors the utility feed, and when grid power is restored to more than 80% voltage, the transfer switch reconnects the panel to the exterior line and shuts down the generator. Automatic switchover is an obvious advantage, but the other primary advantage is that these generators are plumbed to the natural-gas line, so there are no refueling issues. If your area doesn’t have a gas utility, you can convert the engine to run on liquid propane. To decide what size generator and type of backup system will serve your needs best, walk around your house and envision it during a blackout. What damage would occur if the sump pump didn’t work? Would pipes freeze without heat? How much food would DECEMBER 2011/JANUARY 2012 49